Various systems for movably supporting cargo on the floor of cargo holds, such as those found in aircraft, sea-going cargo ships and other cargo-carrying vehicles, have been previously proposed. Typically, such systems include a plurality of roller ball elements mounted on the floor of the cargo hold, thereby providing a low friction support surface over which cargo may be moved. In a typical cargo hold, the floor, and sometimes the walls, are provided with a plurality of elongated trays that are permanently or semi-permanently attached to the floor or other interior surface of the cargo hold. Each tray accommodates one or more ball transfer units, which are removably secured to the trays, thereby permitting the ball transfer units to be replaced when worn or damaged.
While prior systems may have certain functional and useful features, many of the prior system suffer from common shortcomings. For example, it is not uncommon for cargo holds in vehicles to be subject to the periodic ingress of water, dirt or other contaminants. As a result, many prior designs are prone to contamination and may act as receptacles for unwanted water. As dirt, dust and other debris find their way into cargo holds, prior designs have a tendency to allow, or even facilitate, the entry of such contaminants into the ball transfer units. At some point, oxidation of the internal components of ball transfer units may occur, and the collection and concentration of debris in the interior of the units may significantly increase the internal friction occurring within the units, which may render them inefficient and make it difficult for cargo to be easily moved over the ball transfer assemblies. In addition, many prior devices have seams on their upper surfaces that may provide opportunities for cargo to get caught and immobilized during the loading and unloading processes of the cargo bay.
Additionally, currently known products are typically manufactured from metal castings. The loads imposed on ball transfer units by movement of cargo over such units are substantial, sometimes concentrating hundreds of pounds per square inch of load to an individual ball transfer unit. It is not uncommon for cast units to fracture under these loads, rendering the damaged ball transfer unit useless.
There is a need, therefore, for an improved ball transfer unit which restricts the ingress of water, contaminating fluids, dirt, dust and other debris, which present a smooth and unobstructed surface to minimize unintentional interference between the ball transfer unit and cargo being moved there over, and for a ball transfer unit design being constructed from machined versus cast materials to enhance the overall strength of the unit, thereby increasing its durability and useful life.